I don't know about anyone else, but I collect certain vanities such minions, mounts, and bardings. Because of how these items are used, basically they become attached to your character after use. The problem is, my tiny little pudding brain can only retain so much info, so when I look at the MB for minions, I go "aww cute" and buy one, then two months later I see it again, go "aw cute" and buy it again, but because I've already learned it, I have to deal with relisting it, probably out some gil (I'm cheap!), and stuff.
What I'm proposing is that, in the description box (not sure proper name but it tells you what it is, gives some story, etc), rather than telling us how many we carry, tell us if we already own it. Maybe even addition to the part that tells you how many are in your possession (again, pudding brain here).
"But Violyre, why don't you just go check your minions/mounts/bardings lists right before you buy?" you may ask.
You're right, I could! This is one of those little QoL suggestions though.